1. Field of the Invention
The present invention relates to a method for controlling a low noise amplifier (LNA) gain state; and, more particularly, to a method for controlling an LNA gain state in order to improve receiver performance of a mobile terminal in a receiver electric-field environment where the LNA gain state is continuously changed.
2. Description of Related Art
Generally, a low noise amplifier (LNA) in a mobile terminal outputs an inter modulation distortion (IMD) component when two continuous waves are inputted. Such an IMD component distorts signals processed in the mobile terminal and it has become a major problem of signal processing in the mobile terminal causing degradation of the mobile terminal.
When two signals of frequency f1 and f2 are inputted in to the LNA, a component of frequency outputted from the LNA can be represented as mf1±nf2, wherein m and n are positive integers over 1. As the LNA gain increases, an influence of third components (i.e., 2f1−f2 and 2f2−f1) of the IMD component increases to triple times. Therefore, a variable-gain LNA is adapted in order to decrease the LNA gain in a high electric-field as shown in FIG. 1.
Generally, states of the mobile terminal include a sleep mode and an idle mode in order to decrease battery consumption. When the mobile terminal is in the sleep mode, the transmitter and the receiver of the mobile terminal are deactivated and most circuits including a mobile terminal model (MDM) work in a low power consumption mode. Moreover, when the mobile terminal is in the idle mode, the receiver is activated to receive a call from a base station but the transmitter is deactivated.
A state of a code division multiple access (CDMA) mobile terminal switches to the sleep mode or to the idle mode in different ratio according to a slot cycle index (SCI). For example, when the SCI is 0, the mobile terminal switches to the idle mode during 1 slot of total 16 slots (wherein, 1 slot is 80 ms) and remains in the sleep mode during the other 15 slots. In the same manner, when the SCI is 1, the mobile terminal switches to the idle mode during 1 slot of total 32 slots and remains in the sleep mode during the other 31 slots. When a SCI is 2, the mobile terminal switches to the idle mode during 1 slot of total 64 slots and remains in the sleep mode during the other 63 slots. Herein, the smallest value between the values of the SCI in the mobile terminal and the base station is determined as the value of the SCI. The base station determines time to wake up the terminal from the idle mode according to the determined value of the SCI. As mentioned above, the CDMA terminal switches to the idle mode by controlling the ratio of the sleep mode and the idle mode based on the SCI, to thereby decrease a system load and extend the period of the battery usage.
FIG. 1 is a graph showing a LNA gain state in a calling mode in accordance with prior art.
As shown in FIG. 1, the LNA gain state generally includes 4 steps. A first gain state (0) that is the highest state among the 4 steps and a fourth gain state (3) that is the lowest gain state.
FIG. 2 is a flowchart describing steps for entering a sleep mode in a conventional LNA gain state controlling method.
The LNA gain state of the LNA in the receiver of the mobile terminal is set as the fourth gain state (3) that is the lowest gain state at step S201. Setting up the LAN gain state at step S201 can be performed by following function.
rf_set_Ina_decision_to_low gain_state( );
Then, the mode of the receiver is switched to the sleep mode, i.e., the power down mode at step S202. Setting up the mode at step S202 can be performed by the following function.
rfr_sleep_enable( );
FIG. 3 is a flowchart describing steps for entering an idle mode and activating the LNA and the AGC function in a conventional LNA gain state controlling method.
The LNA gain state of the LNA is set as the fourth gain state (3) that is the lowest gain state at step S301. Setting up the LAN gain state at step S301 can be performed by following function.
rf_set_Ina_decision_to_low_gain_state( );
Then, an automatic gain control (AGC) function is deactivated at step S302. The AGC function is a function for determining an AGC value according to received electric-field intensity and controlling the LNA gain according to the determined AGC value. Setting up the AGC function at step S302 can be performed by the following function.
HWIO_OUTM(AGC_RDWR_CTL, CAGC_AGC_OVRD_M, CAGC_AGC_FRZ_V);
Then, the AGC value is set as a value of the lowest gain state, i.e., the fourth gain state (3) at step S303. Setting up the AGC value at step S303 can be performed by following function.
rf_set_agc_value_to_low_gain( );
Then, the mode of the receiver is switched to the idle mode at step S304. Setting up the mode at step S304 can be performed by following function.
rfr_cdma_wakeup( );
Then, the LNA is activated at step S305. Setting up the LAN gain state at step S305 can be performed by following function.
RF_LNA_STATE_MACHINE_NORMAL( );
Then, the AGC function is activated at step S306. Setting up the AGC function at step S306 can be performed by following function.
HWIO_OUTM(AGC_RDWR_CTL, CAGC_AGC_OVRD_M, CAGC_AGC_NRM_V);
Operations of the above mentioned conventional LNA gain state controlling method are described hereinafter.
A table 1 presents a result of measuring an Ec/Io (in dB) of a pilot channel of the mobile terminal according to intensity of received electric field. The Ec/Io is average energy, wherein Ec is energy integrated during one pseudo noise (PN) chip period and Io is a total receipt power spectrum intensity including a noise measured at an antenna connection. As the Ec/Io increases, a reception rate in a field becomes increased.
TABLE 1−85 dBm−87 dBm−89 dBm−91 dBm−93 dBm−95 dBmFirst gain state−6.0~−7.5−6.0~−7.5−6.0~−7.5−6.0~−7.5−7.0~−8.0 −7.0~−8.0 Second gain state−7.0~−8.0−7.0~−8.0−7.5~−8.5−8.0~−9.0−8.5~−10.0−9.5~−11.0
By Referring to an embodiment of the prior art with LNA gain state in an idle mode, it can be estimated that a gain is switched at a specific electric field value (which will be referred to as a switching point hereinafter) because the terminal operates as the gain state is switched from the high electric-field in the conventional idle mode.
It is assumed that a switching point at which the LNA switches from the first gain state to the second gain state is −91 dBm. When the electric-field value is −93 dBm, the receiver wakes up in the idle mode from the sleep mode.
Under the above assumption, if the electric-field value becomes strong as −89 dBm after the receiver wakes up in the idle mode, the LNA switches to the second gain state.
Then, the LNA gain is switched according to FIG. 1. Because a hysterisis range, where the first gain state (0) is changed to the second gain state (1), is from −91 dBm to −86.2 dBm, the second gain state (1) is maintained while the electric-field value is weaker than −91 dBm.
If the receiver does not switch to the sleep mode, the first gain state (0) is maintained although the electric-field value becomes −89 dBm according to FIG. 1.
As referring to the table 1, the Ec/Io becomes increased by 1.5 bB since the mode is switched to the sleep mode under the above assumption and thereby the reception rate becomes decreased.
As mentioned above, the LNA gain state of the LNA in the receiver of the mobile terminal is forcibly switched to the fourth gain state (3) when the mode is switched from the idle mode to the sleep mode. Therefore, when the mode is switched back from the sleep mode to the idle mode, the LNA gain is controlled like the LNA gain is controlled in the high electric-field. Accordingly, if there is the electric-field value in the hysterisis range as shown in FIG. 1, the LNA gain is switched to a state one step lower than the state in the idle mode before the conversion. Therefore, the reception rate becomes degraded.